I. Field of the Invention
The present invention relates to a method and apparatus for growing and conditioning tissue engineered medical products and in particular to a method and apparatus for a servocontrolled bioreactor with a dynamic pressurization system and a chamber with an integrated nutrient reservoir for conditioning tissue engineered medical products (TEMPs) in the orthopedic, secretory organ and vascular areas. TEMPs can include, without limitation, various types of tissue in several areas. Within the orthopedic area TEMPS can include: cartilage, bone, meniscus, ligaments, tendons, muscle, and other musculo-skeletal devices. Within the secretory organ area TEMPs can include liver, kidney, skin and other organs. Within the vascular area TEMPs can include, but are not limited to, heart valves, blood vessels, and cardiac patches. Other TEMPs can include: cornea, bladder, urethra, small intestine or any other tissue that might be replaced in the body.
Tissue engineering is a rapidly growing area that seeks to create, repair and/or replace tissues and organs by using combinations of cells, biomaterials, and/or biologically active molecules. It is an interdisciplinary field that integrates aspects of engineering, and other quantitative sciences, with biology and medicine. Research and technology development in tissue engineering promises to revolutionize current methods of health care treatment and significantly improve the quality of life for millions of patients. As one indication of the scope of the problem that tissue engineering addresses, worldwide organ replacement therapies utilizing standard organo-metallic devices consume 8 percent of medical spending, or approximately $350 billion per year. Organ transplantation is another option for replacing damaged or diseased tissue, but one that is severely limited by donor availability. Tissue-engineered products hold the promise for true functional replacement. However, despite early laboratory successes, few functional tissue engineered products are currently available for clinical use.
Researchers have sought to develop living alternatives to traditional “man-made” medical devices. These TEMPs use the patient's own cells to create replacement devices that can be cultured and grown once they are implanted. Through design and fabrication of biomaterials and specification of cells or biomolecules, it is hoped that TEMPs will play a major role in many future regenerative medicine therapies. In the orthopedic area considerable energy is being expended on the development of tissue engineered cartilage, meniscus, bone, ligaments or tendon replacements. Likewise, similar efforts are being made to develop new replacements for heart valves, arteries, heart muscle tissue and venous valves. Tissue engineered replacements for secretory organs such as the liver, kidney and skin also hold great promise for future therapies. Tissue engineered skin replacements are already available and are dramatically improving the outcomes for patients with diabetic ulcers, as well as burn victims and those undergoing certain cosmetic therapies.
The field of tissue engineering in recent years has included the development of bioreactors which provide a means of conditioning a developing tissue by applying mechanical stresses to a construct (cells or cell seeded substrate while circulating nutrient media around and or through the construct. Cells and tissues grown in bioreactors able to mimic physiological conditions including mechanical forces have enhanced tissue development, mechanical properties and function. These bioreactor systems typically include a bioreactor chamber coupled to a device which generates motion and applies forces, pressures and or deformations to the tissue construct via a mechanical feed-through (push or pull rod). Additionally, these systems typically include a separate reservoir that contains a nutrient media for sustaining the cells within the tissue construct. The reservoir is often connected to the bioreactor chamber via tubing and a mechanical pumping system. The biochemistry of the nutrient media can be maintained by exposing it to the environment that is created within an incubator system. The incubator maintains the temperature, as well as gas concentrations (CO2, O2, etc.). The exposure of the media to the environment is often accomplished by placing a vented reservoir directly in the incubator or by circulating the media through gas permeable tubing located inside the incubator. Gas concentrations can also be bubbled through the media to maintain appropriate culture conditions.
II. Related Art
Other bioreactor systems have addressed aspects of the need for an apparatus dedicated to growing and conditioning tissue engineered medical products. As will become apparent, the present device described in this patent application surpasses those systems in several respects.
Spaulding et al. (U.S. Pat. No. 5,330,908), (U.S. Pat. No. 6,001,643) and Schwartz (U.S. Pat. No. 5,437,998), (U.S. Pat. No. 5,665,594) disclose bioreactor systems that operate at ambient pressure and in which mechanical stresses to the cells are applied by rolling the chamber about its cylindrical axis. Conversely, the bioreactor system of the present invention applies a static or varying pressure to the chamber and subsequently the tissue construct within while the chamber is agitated via a multi-axis motion device.
Dunkleman et al. (U.S. Pat. No. 5,792,603), Peterson et al (U.S. Pat. No. 5,846,828) and Vilendrer et al (U.S. Pat. No. 7,348,175) disclose bioreactor systems for vascular grafts in which an alternating or varying flow or backpressure from an external media storage device is provided via a tube and pumping system. Control of the flow and/or back pressure is provided by an external flow pump. Whereas, in the present system, the sealed chamber and media reservoir are combined thus eliminating the need for an interconnecting tube to create flow. Additionally, pressurization in the present system may be provided directly via a high pressure air source and servovalve controlled by a microprocessor servocontrol system which supplies specific air pressures to one side of a deformable membrane. As the membrane deforms the pressure is transferred to the interior of the chamber. Applegate et al. (U.S. Pat. No. 5,843,766) discloses a bioreactor system for grafts with inlet and outlet ports for evenly distributing media flow across and generally parallel to the tissue substrate that also requires a separate external nutrient fluid reservoir. In the present system, the agitation of the chamber and deformation of the membrane aid in convective mass transport.
Amrani et al. (U.S. Pat. No. 5,902,937) discloses an in vitro testing system for testing blood/tissue interaction that utilizes twin chambers with top and bottom tissue membranes and an internal conduit for conducting blood between the chambers. Blood flow actuation is provided by pistons that alternately depress the membranes on each chamber to displace blood from one chamber to the other. Naughton et al. (U.S. Pat. No. 6,008,049) discloses a diffusion gradient bioreactor system for conditioning tissue engineered liver whereby the tissue is exposed to two nutrient flows. The primary purpose of their device is to move solutes through the device via flow. With the present system only one sealed chamber is needed and it is not interconnected with another chamber to create flow. Also, as indicated above, pressurization in the present invention may be provided directly through a deformable membrane. The high pressure air source is controlled via a microprocessor-controlled servovalve.
Flatt et al (U.S. Pat. No. 6,060,306) discloses a bioreactor chamber with a substrate that is sealed to the sides of the chamber. Using various mechanical actuation means, a pressure differential is created across the substrate to create a fluid flow through it. In the present system, the substrate is not sealed to the sides of the chamber so any applied pressure does not create a differential across the substrate to create a fluid flow through it.
Peterson et al (U.S. Pat. No. 6,121,042) and Carpentier et al (U.S. Pat. No. 6,210,957 B1) disclose bioreactor systems that provide flow about a substrate that is attached to a structure. These systems pump fluid through the chamber using inlet and outlet ports, or actuate the structure to control media flow characteristics around the substrate. In contrast, the substrate of the present system is not attached to a structure but is free to move within the chamber nor is fluid pumped through the chamber to create controlled media flow characteristics. Mechanical agitation of the chamber to enhance fluid mass transport is provided via the shaking motion of a mechanical shaking system and a hydrostatic stress may be provided by pressurization of the membrane as indicated above.
Smith et al (U.S. Pat. No. 6,171,812 B1) and Vilendrer (U.S. Pat. No. 7,410,792 B2) further disclose a bioreactor system that has means for perfusion and application of forces to the substrate within the bioreactor chamber. In the present system, neither of these forces within the chamber is explicitly provided.
Takagi et al (U.S. Pat. No. 6,432,713 B2), (U.S. Pat. No. 6,599,734 B2), (U.S. Pat. No. 6,607,917 B2), (U.S. Pat. No. 6,921,662 B2) describes bioreactor systems which utilize a sealed chamber that is interconnected to a medium reservoir via a tube or circuit. Pressurization of the chambers is provided via actuator driven pistons and control of the system is accomplished using regulators and timers or a microcomputer that turns various valves on at the appropriate times. Tagaki et al (U.S. Pat. No. 7,144,726) also describes a bioreactor chamber with fluid port and a magnetically driven pressing plate for creating pressurization within the chamber. These references do not suggest the use of a sealed combined chamber.
While some of the above described systems have worked in certain applications, there remains a need in the art to simplify the method and apparatus for growing and conditioning tissue while maintaining environmental control.